- Type V collagen is a member of the subclass of fibrillar collagens that is present in minor amounts in virtually all non-cartilaginous connective tissues. As demonstrated by the applicant and others haploinsufficiency of pro-alpha1 (V) collagen chains frequently causes the classical form of Ehlers-Danlos syndrome (EDS I/II) which is characterized by joint laxity and dislocations, severe dermal fragility, and defective wound healing. Therefore, the biomechanical integrity of some connective tissues including skin, tendon, and ligaments appears to be exquisitely sensitive to the quantity of pro-alpha1 (V) chains available to participate in fibrillogenesis, yet other pro-alpha1(V)-containing tissues appear relatively unaffected. Experiments proposed by the applicant are designed to elucidate the role of type V collagen in regulating mechanical properties of tissues. In the first aim the products of pro-alpha1(V) expression genes containing C-propeptide mutations will be analyzed for their ability to self trimerize or to form trimers with wild-type pro-alpha1 (V) chains and pro-alpha2(V) chains. Binding of normal and mutant c-propeptides to chaperone proteins will be analyzed by chemical cross-linking and immunoprecipitation. Fibril shape and deposition of collagens and noncollagenous collagen-binding molecules will be measured in long-term dermal fibroblast cultures. In the second aim the molecular determinants of type V/XI chain selection will be analyzed by trimerization experiments in which full length or minigenes expressing the C-propeptides for pro-alpha1 (V), pro-alpha2 (V), and pro-alpha1 (XI) as well as a novel C-propeptide splice variant of pro-alpha1 (V) will be assembled in vitro and in cellulo after transfection in several cell types having restricted expression of type V/XI collagen chains. In the third aim homozygous and heterozygous col5A1 knockout mice will be analyzed for changes in type-specific collagen deposition in tissues and long-term fibroblast cultures from skin, which is severely affected in human col5A1 haploinsufficiency, and also in cornea, which appears to be spared even though type V collagen's role in collagen fibrillogenesis in cornea is well documented. In the fourth aim fibril morphology, biochemistry, and biomechanical characteristics of cornea and dermis in col5A1-deficient mice will be examined to determine the relationship between total type V collagen content, type V/type XI isoform ratios, noncollagenous protein content, and biomechanical properties.